Wrought Iron

Expounding on a Neat Trick

by Don Friedman on October 30, 2017

I talked a bit about this type of detail recently but I was surprised to learn that I hadn’t posted these pictures. This is a middle-third of the 1800s tenement in Hell’s Kitchen that was built with retail space on the first floor. The wood joists of the floors and roof span left to right, supported by the side walls and two interior walls in line with the two columns on the facade we’re looking at. 

Both street facades are supported on these cast-iron arches tied with wrought-iron rods, and the arches are supported on cast-iron columns. The fascias at the tops of the old storefronts, which probably carried signs for the stores, hid everything from the rods up to the top of the brick band above the arches. I happened to be in the right place, at the right time, with a camera in my hand to get a series of pictures that show the structure exposed. 

It’s not an accident that the arches are so shallow. First, it’s easier to transition from iron to brick if the arch curve is shallow. Second, it was easier to cast the nearly-straight arch pieces than it would have been to cast more curved pieces. Most importantly, the shallower an arch is, the greater its horizontal  thrust, but the use of the wrought-iron ties meant that thrust was not a problem here. 

As I said before, this is a clever detail that uses the commonly-available technology of the era to do something quite difficult: support a masonry wall over a large void. 

156 Years Of Dirt

March 16, 2017

Whatever that light-gray dust is – some combination of rotted wood, ancient coal smoke, and pigeon crap, most likely – it was damned difficult to wash off my hands and shirt. But that’s not the point. What is this thing? It’s the cast-iron arch holding up the rear wall of an 1861 loft building over the […]

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A Subtle Hint

January 24, 2017

That picture was taken in a mid-to-late-nineteenth-century industrial building, on the top floor with only the attic above. The exposed wood beam is about 8 inches wide and 12 inches deep but appears to span some fifty feet, which is obviously ridiculous. The building has a gable roof so the most likely bet is that […]

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June 30, 2016

Know any blacksmiths? There’s a job opening right now with the New York City Department of Parks and Recreation. This might sound like a joke* but it’s serious. Blacksmiths shape iron and steel in complex three-dimensional configurations that are not easily achievable using other methods. The introduction of CAD/CAM cutters allows for extremely complex and […]

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Historic Structural Detail: Geometric Strength

May 26, 2016

Some structural forms are more efficient than others. For example, roof trusses tend to be deep (vertically) relative to their spans. Trusses can be examined at two scales: at a small scale, member by member and connection by connection, or at the overall scale, where they are analogues of beams. It’s at the overall scale […]

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Historic Structural Detail: A Composite Arch

March 16, 2016

One of the earliest challenges for structural engineers – long before the profession formally existed – was how to support masonry walls over openings. The tight column spacing of Greek and Egyptian temples, for example, was based in part on the limited spanning capacity of stone beams. Masonry arches, as used by the Romans, could span […]

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